Microelectromechanical systems (MEMS) technology has been under steady development for some time, and as a result various MEMS devices, including gyroscopes, have been implemented within several applications. MEMS gyroscopes generally belong to a vibratory mass class of gyroscopes.
Typically a vibratory angular rate sensor comprises a single drive and a single sense subsystem. The drive subsystem is driven into oscillation at the resonant frequency of the drive mode. A Coriolis force acts on the oscillating drive subsystem and generates force which is then transferred to the sense subsystem. Consequently, the sense subsystem moves at the drive frequency proportional to the input rate of rotation and that motion is typically sensed by an appropriate transducer.
One problem with this type of sensor is the duplication of driving system and drive electronics. A drive system and sense subsystem is needed for each axis in which angular velocity is desired to be sensed, so that at least three drive systems are needed to cover all three axes.
Some types of angular rate sensors have provided a single drive system with a sensing subsystem that senses in multiple axes. For example, U.S. Patent Publication No. 2007/0220971 by Ayazi et al. describes a single bulk structure driven at multiple drive frequencies and is used to sense three input axes. U.S. Patent Publication No. 2007/0214883 by Durante et al. describes a single structure driven at a single drive frequency and used to sense three input axes. Patent application 20090064780 by Coronato et al. where a single structure driven at single drive frequency is used to sense three input axes. None of these structures use expanding members (an extension mode). Other devices, such as resonators, have been provided with single structures having an expanding member. For example, U.S. Pat. No. 7,323,952 by Pan et al. describes a bulk resonator including a breathing-like mode of expansion thus describing bulk structures and not discrete mass structures. U.S. Pat. Nos. 7,205,867 and 7,227,432 by Lutz et al. describe a resonator including nodal points and “breathing” and “bending” movement. These structures involve nodal points, i.e. points where masses do not move. U.S. Pat. No. 7,363,814 by Okada describes a device having one mass moving in different directions. U.S. Pat. Nos. 6,856,217 and 6,628,177 by Clark et al. describe an expanding resonator for filtering and oscillator applications.
These prior devices are all limited in various ways and none allow for an angular rate sensor using a single drive system moving in an extension mode and multiple masses and which can provide one or more sensing axes.